Experimental and analytical investigation of finger-follower cam systems

Research output: Other contribution

Abstract

A predictive dynamic model to compute the motions of components in cam systems, along with the experimental work to verify the model are described. The major components in finger-follower cam systems include the cam, the follower, the hydraulic lash adjuster, and the valve spring, equipped sometimes with a helical valve spring cup damper. In order to fully describe the dynamics of such a system, a lumped/distributed parameter model for the finger-follower cam system with a moving follower pivot is proposed. The valve spring is modeled as a distributed parameter element, and the adjuster is modeled as a stiff spring with viscous damping. The coulomb friction combined with viscous damping between sliding surfaces are also considered. The model predicts toss between the adjuster and the follower at 2535 rpm, and experiment indicates toss starting at 2520 rpm. It is found by simulation that designing hydraulic lash adjuster to be as rigid as possible is essential to successful high speed operation of finger-follower valve trains because a 50 percent decrease in the compliance of the adjuster could increase the maximum camshaft operating speed 150 rpm. Total elimination of the hydraulic lash adjuster is not always feasible because hydraulic lash adjusters can eliminate the clearance between components and do not need to be mechanically, manually adjusted. In order to provide a more stable and precise description on the dynamic response of the adjuster, a two-mode dynamic model for the adjuster is proposed by considering the oil compressibility in the oil chamber, as well as the oil leakage through the annular gap. Furthermore, the effect due to the oil flow from the central orifice to the oil chamber is also studied analytically and experimentally. The inertia effects of the helical valve spring can be suppressed by a cup damper. Damping between the damper and spring wire is found to depend only weakly on relative sliding velocity. The current formula in computing spring force including the effects of coulomb friction, spring coil dilation, bending moments on both the spring wire and the damper, is verified by comparison between different models and experimental data.
Original languageEnglish
TypePh.D. Thesis
Number of pages1
StatePublished - 1992

Keywords

  • Cams
  • Dynamic Models
  • Dynamic Response
  • Hydraulic Equipment
  • Simulation
  • Viscous Damping
  • Bending Moments
  • Friction
  • Sliding
  • Mechanical Engineering

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